For all types of substrates, magnetic recording media has begun to incorporate perpendicular magnetic recording (PMR) technology in an effort to increase areal density. Generally, PMR media may be partitioned into two primary functional regions: a soft underlayer (SUL) and a magnetic recording layer(s) (RL). FIG. 1 illustrates portions of a conventional PMR disk drive system having a recording head 101 including a trailing write pole 102 and a leading return (opposing) pole 103 magnetically coupled to the write pole 102. An electrically conductive magnetizing coil 104 surrounds the yoke of the write pole 102. The bottom of the opposing pole 103 has a surface area greatly exceeding the surface area of the tip of the write pole 102. As the magnetic recording disk 105 is rotated past the recording head 101, current is passed through the coil 104 to create magnetic flux within the write pole 102. The magnetic flux passes from the write pole 102, through the magnetic recording disk 105, and across to the opposing pole 103 to record in the PMR layer 150. The SUL 110 enables the magnetic flux from the trailing write pole 102 to return to the leading opposing pole 103 with low impedance.
With the advent of heat-assisted magnetic recording (HAMR) media, areal density in hard disk drives can be extended beyond 1.5 Tb/in2. However, superparamagnetic limits, thermal stability, and writability issues can limit the ability to increase areal densities in hard disk drives using conventional PMR media. Thus, and in order to support higher areal densities while also providing thermal stability, HAMR media is often made of magnetic materials or compounds with substantially higher magnetocrystalline anisotropy (indicated by the magnetic anisotropy constant, Ku) than that of non-HAMR media (e.g., Cobalt-Chromium-Platinum (CoCrPt) alloys). One example of such an alloy having substantially higher magnetocrystalline anisotropy is the L10 phase of Iron-Platinum (FePt) alloys. In principle, the higher Ku of L10 FePt allows grains as small as 2-5 nm to remain thermally stable. Unlike CoCrPt alloys however, the growth of chemically ordered L10 FePt requires a deposition temperature greater than 400° C. Moreover, due to the limitations in available writing fields, a write assist mechanism, such as HAMR is needed for high Ku media. Additionally still, HAMR media with a SUL typically has a wider magnetic write width (MWW) than media without a SUL, thereby limiting its areal density capabilities.
Because HAMR media is made of higher-stability magnetic compounds, as described above, HAMR media relies upon the application of heat to achieve changes in magnetic orientation. HAMR media is temporarily heated to reduce its coercivity below that of an applied magnetic write field from a recording head, i.e., the temperature of the recording location on the HAMR media is increased in order to sufficiently lower the location's Ku to allow a change to its magnetic orientation (i.e., record data). This allows for higher media anisotropy and smaller thermally stable grains.